<template>
   <scroll :data="data" 
          ref="listview"
          class="listview"
          :listenScroll = "listenScroll"
          @scroll="scroll"
          :probeType="probeType">    
        <ul>
          <li v-for="group in data" :key="group.title" class="list-group" ref="listGroup">
            <h2 class="list-group-title">{{group.title}}</h2>
            <ul>
              <li @click="selectItem(item)" v-for="item in group.items" :key="item.id" class="list-group-item">
                <img v-lazy="item.avater" class="avatar"/>
                <span class="name">{{item.name}}</span>
              </li>
            </ul>
          </li>
        </ul>
        <div class="list-shortcut" @touchstart="onShortcutTouchStart" @touchmove.stop.prevent="onShortcutTouchMove">
          <ul>
            <li v-for="(item,index) in shortCutList" 
            :data-index="index" :key="item" class="item" :class="{'current':currentIndex===index}">
              {{item}}
            </li>
          </ul>
        </div>  
        <div class="list-fixed" v-show="fixedTitle" ref="fixed">
          <h1 class="fixed-title">{{fixedTitle}}</h1>
        </div>  
        <div v-show="!data.length" class="loading-container">
          <loading></loading>
        </div>    
    </scroll>  
</template>
<script type="text/ecmascript-6">
import {getData} from 'common/js/dom'
import Scroll from 'base/scroll/scroll'
import Loading from 'base/loading/loading'
import { parse } from 'semver';
import { setTimeout } from 'timers';
const ANCHOR_HEIGHT = 18
const TITLE_HEIGHT = 30
  export default {
    created() {
      this.touch = {},
      this.listenScroll= true,
      this.listHeight = [],
      this.probeType  = 3
    },

    components:{
      Scroll,
      Loading
    },
    props: {
      data: {
        type :Array,
        default:[]
      }
    },
    data (){
      return {
        scrollY : -1,
        currentIndex :0,
        diff:-1
      }
    },
    methods :{
      selectItem(item) {
        this.$emit('select', item)
      },
      onShortcutTouchStart(e) {
        let anchorIndex = getData(e.target,'index')
        let firstTouch = e.touches[0]
        this.touch.y1 = firstTouch.pageY //得到第一个滚动的为位置
        this.touch.anchorIndex = anchorIndex
        this._scrollTo(anchorIndex)
        
      },
      onShortcutTouchMove(e) {
        let firstTouch = e.touches[0]
        this.touch.y2 = firstTouch.pageY
        let delta = (this.touch.y2 - this.touch.y1)/ANCHOR_HEIGHT | 0
        let anchorIndex =parseInt(this.touch.anchorIndex ) + delta
        this._scrollTo(anchorIndex)

      },
      _scrollTo(index) {
        if(!index && index!==0) {
          return
        }
        if(index < 0){
          index =0
        }else if(index > this.listHeight.length-2){
          index = this.listHeight.length-2
        }
        this.scrollY = -this.listHeight[index]
          this.$refs.listview.scrollToElement(this.$refs.listGroup[index],0)
      },
      scroll(pos) {
        this.scrollY = pos.y//实时获取滚动y轴的距离
      },
      _calculateHeight() {//计算每个group的高度
        this.listHeight = []
        const list = this.$refs.listGroup
        let height = 0
        this.listHeight.push(height)
        for(let i=0;i<list.length;i++) {
          let item = list[i]
          height += item.clientHeight
          this.listHeight.push(height)
        }
      }
      
    },
    watch :{
      data () {
        setTimeout(() => {
          this._calculateHeight()
        },20)
      },
      scrollY(newY) {
        const listHeight = this.listHeight
        //当滚动到顶部，newY>0
        if(newY>0) {
          this.currentIndex = 0
          return
        }
        //在中间部分滚动
        for(let i=0;i<listHeight.length-1;i++) {
          let height1 = listHeight[i]
          let height2 = listHeight[i+1]
          if (-newY >= height1 && -newY<height2){
            this.currentIndex = i
            this.diff = height2 + newY
            return
          }
        }
        //滚动到底部，且-newY大于最后一个元素的上限
        this.currentIndex = listHeight.length -2
      },
      diff(newVal) {
        let fixedTop = (newVal > 0 && newVal < TITLE_HEIGHT) ? newVal - TITLE_HEIGHT : 0
        if (this.fixedTop === fixedTop) {
          return
        }
        this.fixedTop = fixedTop
        this.$refs.fixed.style.transform = `translate3d(0,${fixedTop}px,0)`
      }
    },
    computed :{
      shortCutList() {
        return this.data.map((group) => {
          return group.title.substr(0,1)
        })
      },
      fixedTitle() {
        if(this.scrollY >= -1){
          return ''
        }
        return this.data[this.currentIndex]? this.data[this.currentIndex].title :''
      }   
    }
  }
</script>

<style scoped lang="stylus" rel="stylesheet/stylus">
  @import "~common/stylus/variable"
  .listview
    position: fixed
    width: 115%
    height: 100%
    overflow: hidden
    margin-left :-40px
    background: $color-background
    .list-group
      padding-bottom: 30px
      .list-group-title
        height: 30px
        line-height: 30px
        padding-left: 20px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
      .list-group-item
        display: flex
        align-items: center
        padding: 20px 0 0 30px
        .avatar
          width: 50px
          height: 50px
          border-radius: 50%
        .name
          margin-left: 20px
          color: $color-text-l
          font-size: $font-size-medium
    .list-shortcut
      position: fixed
      z-index: 30
      right: 0
      top: 50%
      width :20px
      transform: translateY(-50%)
      padding: 20px 0
      border-radius: 10px
      text-align: center
      background: $color-background-d
      font-family: Helvetica
      .item
        margin-left :-60px
        padding: 3px
        line-height: 1
        color: $color-text-l
        font-size: $font-size-small-s
        list-style-type:none
        &.current
          color: $color-theme
    .list-fixed
      position: absolute
      margin-top :-10px
      top: 0
      left: 0
      width: 100%
      .fixed-title
        height: 30px
        line-height: 30px
        padding-left: 60px
        font-size: $font-size-small
        color: $color-text-l
        background: $color-highlight-background
    .loading-container
      position: absolute
      width: 100%
      top: 50%
      transform: translateY(-50%)
</style>
